This invention relates to a solid electrolytic capacitor of the type containing within itself a circuit-opening mechanism such as a fuse. More particularly, the invention relates to such a solid electrolytic capacitor which can be designed to make its casing smaller or its capacitor element larger for the same size of its casing.
FIG. 4 shows an example of prior art solid electrolytic capacitor with a capacitor element 21 formed by subjecting a sintered body of valve action metallic powder such as tantalum powder to various treatment processes including chemical conversion process. A lead 22 is inserted into one of side surfaces of this capacitor element 21 to serve as its positive electrode, while its outer surface serves as its negative electrode. A first lead line 23 and a second lead line 24 are respectively connected electrically to the positive electrode 22 and the negative electrode. These electrodes are encapsulated inside a casing 26 of a resin material. The solid electrolytic capacitor thus structured has a definite polarity such that it will be short-circuited if it is connected in a wrong direction. In such a situation, not only may the capacitor heat up or become ignited but other electronic components of the circuit in which this solid electrolytic capacitor is incorporated may also be damaged. In view of such possibilities, a circuit-opening mechanism such as a fuse is frequently provided on the side of either the positive electrode or the negative electrode such that the circuit will open between the lead lines 23 and 24 in an abnormal situation. In order to make its connection easier, it has been known to provide a fuse 25 in the shape of a wire or a ribbon on the side of the negative electrode, as shown in FIG. 4. connecting between the negative electrode on the outer surface of the capacitor element 21 and the second lead line 24, being attached to them, say, be compression.
With the recent trend to miniaturize electronic components, it is becoming necessary to provide miniaturized tantalum capacitors. It is not desirable, however, to reduce the size of the casing 26 merely by making the capacitor element 21 smaller because this would adversely affect the electrical characteristic of the capacitor such as its capacitance. Instead, what is desirable is to reduce the size of the casing 26 while maintaining the electrical characteristic of the capacitor high by not making the capacitor element 21 smaller, or keeping the capacitor element 21 as large as possible.
For connecting the fuse 25 between the outer wall of the capacitor element 21 and the second lead line 24, however, the fuse 25 is usually formed in a smoothly arcuate shape, as shown in FIG. 4, because a fuse having a sharply bent portion would more easily come off the capacitor element 21 or the second lead line 24 to which it is attached by compression. If the fuse 25 is to have a slowly curving shape between the outer surface of the capacitor element 21 and the second lead line 24, however, the distance between the capacitor element 21 and the second lead line 24 as well as the distance between the capacitor element 21 and the upper surface of the casing 26 must be made sufficiently large, and this results in many wasteful spaces. Thus, there was a limit to how large the capacitor element could be made in order to improve the electrical characteristics of the capacitor while the size of the casing was kept fixed, or how small the capacitor could be made for a capacitor element of the same size with the same electrical characteristic. In other words, prior art solid electrolytic capacitors as shown in FIG. 4 could not satisfy the current demand for miniaturized high-quality electronic components.